Method and apparatus for signal detection and decoding

ABSTRACT

A method, apparatus and computer program product are provided herein for enabling the joint detection and decoding of uplink state flag symbols. In this regard, a method is provided that determining one or more residual error terms by jointly detecting and decoding in one or more bursts of a radio block. In some example embodiments, the one or more residual error terms are determined over a plurality of uplink state flag symbols in the one or more bursts that correspond to a plurality of available uplink state flag sequences. The method of this embodiment may also include determining a weighted error measure for each of the plurality of available uplink state flag sequences based on the one or more residual error terms. The method of this embodiment may also include determining an uplink state flag value based on the plurality of weighted error measures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to UK Application No. 1217885.1, filedOct. 5, 2012, which is hereby incorporated herein in its entirety byreference.

TECHNICAL FIELD

Embodiments of the present invention relate generally to communicationstechnology and, more particularly, to example signal detection anddecoding.

BACKGROUND

The modern computing era has brought about a tremendous expansion incomputing power as well as increased affordability of computing devices.This expansion in computing power has led to a reduction in the size ofcomputing devices and given rise to a new generation of mobile devicesthat are capable of performing functionality that only a few years agorequired processing power provided only by the most advanced desktopcomputers. Consequently, mobile computing devices having a small formfactor have become ubiquitous and are used by consumers of allsocioeconomic backgrounds.

As a result of the expansion in computing power and reduction in size ofmobile computing devices, mobile computing devices are being marketedwith an ever increasing array of features. For example, communicationsystems, such as the Global System for Mobile Communications (GSM®), arecontinuously evolving to include additional features and increased datarates. One such example of the ability to provide increased data ratesin GSM is the Enhanced General Packet Radio Service (EGPRS) and relatedextension EGPRS2. In some examples, EGPRS and EGPRS2 are configured toemploy Uplink State Flag (USF) symbols to specify an instance in which acommunication device is permitted to transmit data. For example, at agiven time, an uplink resource may be allocated to the communicationdevice in the GSM system as signaled via the USF value.

In some examples, the communication device is configured to decode theUSF symbols received in a radio block from a base station. In aninstance in which the decoded USF value matches the allocated USF, thecommunication device is then, for example, permitted to cause thetransmission of data.

In order to prevent the communication device from transmitting data inan incorrect uplink resource or at a time when the uplink resources hasnot been allocated, the USF value is configured to be detected reliablyin instance in which it is transmitted by the base station. In somecases, the 3rd Generation Partnership Project (3GPP) has established aminimum USF detection performance. The performance requirements are atleast partially defined in 3GPP TS 45.003, which is incorporated byreference in its entirety herein.

SUMMARY

In some example embodiments, a method is provided that comprisesdetermining one or more residual error terms by jointly detecting anddecoding in one or more bursts of a radio block. In some exampleembodiments, the one or more residual error terms are determined over aplurality of uplink state flag symbols in the one or more bursts thatcorrespond to a plurality of available uplink state flag sequences. Themethod of this embodiment also includes determining a weighted errormeasure for each of the plurality of available uplink state flagsequences based on the one or more residual error terms. The method ofthis embodiment also includes determining an uplink state flag valuebased on the plurality of weighted error measures.

In further example embodiments, an apparatus is provided that includes aprocessing system, which may be embodied by at least one processor andat least one memory including computer program code. The processingsystem is arranged to cause the apparatus to at least determine one ormore residual error terms by jointly detecting and decoding in one ormore bursts of a radio block. In some example embodiments, the one ormore residual error terms are determined over a plurality of uplinkstate flag symbols in the one or more bursts that correspond to aplurality of available uplink state flag sequences. The processingsystem is also arranged to cause the apparatus to determine a weightederror measure for each of the plurality of available uplink state flagsequences based on the one or more residual error terms. The processingsystem is also arranged to cause the apparatus to determine an uplinkstate flag value based on the plurality of weighted error measures.

In yet further example embodiments, a computer program product may beprovided that includes at least one non-transitory computer-readablestorage medium having computer-readable program instructions storedtherein with the computer-readable program instructions includingprogram instructions, which, when executed by an apparatus, causes theapparatus to perform the steps of: determining one or more residualerror terms by jointly detecting and decoding in one or more bursts of aradio block; determining a weighted error measure for each of theplurality of available uplink state flag sequences based on the one ormore residual error terms; and determining an uplink state flag valuebased on the plurality of weighted error measures. In some exampleembodiments, the one or more residual error terms are determined over aplurality of uplink state flag symbols in the one or more bursts thatcorrespond to a plurality of available uplink state flag sequences.

In yet further example embodiments, an apparatus is provided thatincludes means for determining one or more residual error terms byjointly detecting and decoding in one or more bursts of a radio block.In some example embodiments, the one or more residual error terms aredetermined over a plurality of uplink state flag symbols in the one ormore bursts that correspond to a plurality of available uplink stateflag sequences. The apparatus of this embodiment also includes means fordetermining a weighted error measure for each of the plurality ofavailable uplink state flag sequences based on the one or more residualerror terms. The apparatus of this embodiment also includes means fordetermining an uplink state flag value based on the plurality ofweighted error measures.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the example embodiments of the invention ingeneral terms, reference will now be made to the accompanying drawings,which are not necessarily drawn to scale, and wherein:

FIG. 1 is a schematic representation of a system having a communicationdevice that may be configured for reference symbol sequence allocationand that may benefit from some example embodiments of the presentinvention;

FIG. 2 is a block diagram of an apparatus that may be embodied by acommunication device and/or an base station in accordance with someexample embodiments of the present invention;

FIG. 3 a illustrates an example burst structure for EGPRS2A in DAS-7 toDAS-12;

FIG. 3 b illustrates the burst structure for EGPRS2B in DBS-5 to DBS-12;and

FIG. 4 is a flow chart illustrating operations performed by an examplecommunication device in accordance with some example embodiments of thepresent invention.

DETAILED DESCRIPTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments of the inventions are shown. Indeed, these inventions may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements throughout.

As used in this application, the term “circuitry” refers to all of thefollowing: (a) hardware-only circuit implementations (such asimplementations in only analog and/or digital circuitry) and (b) tocombinations of circuits and software (and/or firmware), such as (asapplicable): (i) to a combination of processor(s) or (ii) to portions ofprocessor(s)/software (including digital signal processor(s)), software,and memory(ies) that work together to cause an apparatus, such as amobile phone or server, to perform various functions) and (c) tocircuits, such as a microprocessor(s) or a portion of amicroprocessor(s), that require software or firmware for operation, evenif the software or firmware is not physically present.

This definition of “circuitry” applies to all uses of this term in thisapplication, including in any claims. As a further example, as used inthis application, the term “circuitry” would also cover animplementation of merely a processor (or multiple processors) or portionof a processor and its (or their) accompanying software and/or firmware.The term “circuitry” would also cover, for example and if applicable tothe particular claim element, a baseband integrated circuit orapplication specific integrated circuit for a mobile phone or a similarintegrated circuit in server, a cellular network device, or othernetwork device.

Each of EGPRS, EGPRS2A and EGPRS2B comprise a plurality of modulationschemes, for example, a modulation scheme used in accordance with EGPRSmay include Gaussian Minimum-Shift Keying (GMSK), 8-Phase-Shift Keying(8PSK) modulation and/or the like. In some examples, the modulation usedin EGPRS2 may also include Quadrature Phase-Shift Keying (QPSK), 16- and32-Quadrature Amplitude Modulation (QAM) and/or the like.

Further, and in some examples, each of EGPRS, EGPRS2A and EGPRS2B defineone or more modulation and coding schemes. For example, EGPRS isconfigured to operate ten modulation and coding schemes (MCS-0 toMCS-9). In EGPRS2A, for example, eight modulation and coding schemes(DAS-5 to DAS-12) have been specified. In EGPRS2B, for example, eightadditional modulation and coding schemes have been specified (DBS-5 toDBS-12). Other modulation and coding schemes may also be made availablein accordance with the example modulation and coding schemes defined.

In some examples, EGPRS and EGPRS2, as described with reference to GSM,may include a plurality of different USF bit sequences that can betransmitted to one or more communication devices, such as via a basestation. In some examples, the plurality of USF bit sequences may bedefined as eight USF bit sequences that are associated with the burstsavailable in a radio frame in accordance with an example Time DivisionMultiple Access (TDMA) scheme. Other bit sequences and/or flags may beused with respect to alternative communication systems.

EGPRS and EGPRS2 each define a burst structure. In the burst structure,in some examples, the USF symbols are located to the right of theTraining Sequence Code (TSC). For example, in EGPRS2A DAS-7 to DAS-12,the burst structure includes a tail of 3 symbols, followed by 58 symbolsof other user data and/or payload, followed by 26 TSC symbols, then 3USF symbols, followed by 55 other user data and/or payload symbols andthen 3 tail symbols before the guard period. By way of further example,in EGPRS2B DBS-5 to DBS-12 includes a tail of 4 symbols, followed by 69symbols of other user data and/or payload, followed by 31 TSC symbols,then 4 USF symbols, followed by 65 other user data and/or payloadsymbols and then 4 tail symbols before the guard period. See e.g. FIGS.3 a and 3 b.

In some examples, the channel coding used in USF for MCS-5 to MCS-9(8PSK) comprises a (36, 3) block code. A (36, 3) block code, forexample, describes an instance in which 3 USF bits are encoded to 36 USFbits that are spread across 4 bursts of a radio block, such that 9 USFbits are transmitted per burst. In this example coding, the USF bits ineach burst, for example, are located at the bit positions [150, 151,168, 169, 171, 172, 177, 178, 195] before the modulation mapping (forexample, mapping from bits to symbols).

In EGPRS2A, for example, the number of USF symbols per burst is 3, whichresults in 9 bits that are transmitted per burst for DAS-5 to DAS-7. Insome examples, DAS-5 to DAS-7 (8PSK) uses the same USF bit mapping on aburst as for example MCS-5. DAS-8 to DAS-9 (16QAM) uses, for example, 12bits per burst, which are placed at bit positions [232-243]. In furtherexamples, the USF symbols in DAS-10 to DAS-12 (32QAM) are also, forexample located next to, to the right of or otherwise after the TSC inthe burst, since the 15 USF bits per burst are placed at positions[290-304].

In some examples and in EGPRS2B the number of USF symbols per burst is4. For DBS-5 to DBS-6 (QPSK) the 8 USF bits per burst are placed, forexample, at bit positions [138-145]. For DBS-7 to DBS-9 (16QAM) the 16USF bits are placed, for example at bit positions [276-291], further the20 USF bits per burst in DBS-10 to DBS-12 (32QAM) are placed at bitpositions [345-364]. Thus, for DBS-5 to DBS-12 the USF symbols are alsolocated to the right, after or otherwise next to the TSC symbols.

As described herein, the performance requirements for detection anddecoding of the USF symbols are strictly defined. As such in someexample embodiments, the method, apparatus and computer program productas is described herein enable the joint detection and decoding of theUSF. In some example embodiments, the location of the USF symbols,positioned after, next to or to the right of the TSC in a burstadvantageously, for example, enables the joint detection and decodingwithin the defined performance requirements. In some example embodimentsand based on a location of the USF symbols, the interfering symbols fromthe TSC are determined. For example, USF joint detection and decodingcan be achieved by evaluating and comparing a metric for the availableUSF sequences defined by EGPRS and EGPRS2 while taking the Inter SymbolInterference (ISI) from TSC symbols into account. Additionally, in someexample embodiments and in an instance in which equalization has alreadybeen conducted, additional symbols positioned after, next to, or to theright of, the USF symbols in the burst (for example the payload symbols)may also be utilized when decoding the USF. In some example embodiments,the USF sequence with the best fit (e.g. measured by the smallestweighted squared error and/or the like) is selected as the bestcandidate for the USF sequence, and the uplink state flag value ischosen accordingly. Additionally, in some example embodiments averification of the reliability of the detected USF value can beperformed, for example based on the determined fit of the USF sequences.

A method, apparatus and computer program product are provided herein forenabling the joint detection and decoding of uplink state flag symbols.In this regard, a method is provided that computes one or more residualerror terms over one or more time indices in one or more bursts of aradio frame for a plurality of available uplink state flag symbols thatcorresponds to a plurality of available uplink state flag sequences. Theresidual error terms are computed while taking the inter symbolinterference contribution from the received training sequence code intoaccount. The method of this embodiment may also determine a weightederror measure for each of the plurality of available uplink state flagsequences based on the one or more available error terms from one ormore bursts. The method of this embodiment may also select the uplinkstate flag value based on the weighted error measure associated with theplurality of available uplink state flag sequences and may ensure thatthe uplink state flag value is reliably detected.

Although the method, apparatus and computer program product as describedherein may be implemented in a variety of different systems, one exampleof such a system is shown in FIG. 1, which includes a communicationdevice (e.g., communication device 10) that is capable of communicationvia a base station 12, such as an access point, a macro cell, a Node B,an eNB, Base Transceiver Station (BTS), a coordination unit, a macrobase station or other access point, with a network 14 (e.g., a corenetwork). While the network may be configured in accordance with GSM,other networks, such as LTE™ or LTE-Advanced (LTE-A™), may support themethod, apparatus and computer program product of some embodiments ofthe present invention including those configured in accordance withwideband code division multiple access (W-CDMA™), CDMA2000, generalpacket radio service (GPRS™), IEEE™ 802.11 standard for wirelessfidelity (WiFi), wireless local access network (WLAN™) WorldwideInteroperability for Microwave Access (WiMAX™) protocols, and/or thelike.

The network 14 may include a collection of various different nodes,devices or functions that may be in communication with each other viacorresponding wired and/or wireless interfaces. For example, the network14 may include one or more cells, including base station 12, which mayserve a respective coverage area. The base station 12 may be, forexample, part of one or more cellular or mobile networks or public landmobile networks (PLMNs). In turn, other devices such as processingdevices (e.g., personal computers, server computers or the like) may becoupled to the communication device 10 and/or other communicationdevices via the network 14.

A communication device, such as the communication device 10 (also knownas user equipment (UE), a mobile terminal or the like), may be incommunication with other communication devices or other devices via thebase station 12 and, in turn, the network 14. In some cases, thecommunication device 10 may include an antenna or a plurality ofantennas for transmitting signals to and for receiving signals from anbase station 12.

In some example embodiments, the communication device 10 may be a mobilecommunication device such as, for example, a mobile telephone, portabledigital assistant (PDA), pager, laptop computer, STA, or any of numerousother hand held or portable communication devices, computation devices,content generation devices, content consumption devices, or combinationsthereof. Other such devices that are configured to connect to thenetwork include, but are not limited to a refrigerator, a securitysystem, a home lighting system, and/or the like. As such, thecommunication device 10 may include one or more processors that maydefine processing circuitry and a processing system, either alone or incombination with one or more memories. The processing circuitry mayutilize instructions stored in the memory to cause the communicationdevice 10 to operate in a particular way or execute specificfunctionality when the instructions are executed by the one or moreprocessors. The communication device 10 may also include communicationcircuitry and corresponding hardware/software to enable communicationwith other devices and/or the network 14.

In one embodiment, for example, the communication device 10 and/or thebase station 12 may be embodied as or otherwise include an apparatus 20as generically represented by the block diagram of FIG. 2. While theapparatus 20 may be employed, for example, by a communication device 10or a base station 12, it should be noted that the components, devices orelements described below may not be mandatory and thus some may beomitted in certain embodiments. Additionally, some embodiments mayinclude further or different components, devices or elements beyondthose shown and described herein.

As shown in FIG. 2, the apparatus 20 may include or otherwise be incommunication with processing circuitry 22 that is configurable toperform actions in accordance with example embodiments described herein.The processing circuitry may be configured to perform data processing,application execution and/or other processing and management servicesaccording to an example embodiment of the present invention. In someembodiments, the apparatus or the processing circuitry may be embodiedas a chip or chip set. In other words, the apparatus or the processingcircuitry may comprise one or more physical packages (e.g., chips)including materials, components and/or wires on a structural assembly(e.g., a baseboard). The structural assembly may provide physicalstrength, conservation of size, and/or limitation of electricalinteraction for component circuitry included thereon. The apparatus orthe processing circuitry may therefore, in some cases, be configured toimplement an embodiment of the present invention on a single chip or asa single “system on a chip.” As such, in some cases, a chip or chipsetmay constitute means for performing one or more operations for providingthe functionalities described herein.

In an example embodiment, the processing circuitry 22 may include aprocessor 24 and memory 28 that may be in communication with orotherwise control a communication interface 26 and, in some cases, auser interface 29. As such, the processing circuitry may be embodied asa circuit chip (e.g., an integrated circuit chip) configured (e.g., withhardware, software or a combination of hardware and software) to performoperations described herein. However, in some embodiments taken in thecontext of the communication device 10, the processing circuitry may beembodied as a portion of a mobile computing device or other mobileterminal. In some examples, the processing circuitry 22 and/or theprocessor 24 make take the form of a processing system in some exampleembodiments.

The user interface 29 (if implemented) may be in communication with theprocessing circuitry 22 to receive an indication of a user input at theuser interface and/or to provide an audible, visual, mechanical or otheroutput to the user. As such, the user interface may include, forexample, a keyboard, a mouse, a trackball, a display, a touch screen, amicrophone, a speaker, and/or other input/output mechanisms. Theapparatus 20 need not always include a user interface. For example, ininstances in which the apparatus is embodied as a base station 12, theapparatus may not include a user interface. As such, the user interfaceis shown in dashed lines in FIG. 2.

The communication interface 26 may include one or more interfacemechanisms for enabling communication with other devices and/ornetworks. In some cases, the communication interface may be any meanssuch as a device or circuitry embodied in either hardware, or acombination of hardware and software that is configured to receiveand/or transmit data from/to a network 14 and/or any other device ormodule in communication with the processing circuitry 22, such asbetween the communication device 10 and the base station 12. In thisregard, the communication interface may include, for example, an antenna(or multiple antennas) and supporting hardware and/or software forenabling communications with a wireless communication network and/or acommunication modem or other hardware/software for supportingcommunication via cable, digital subscriber line (DSL), universal serialbus (USB), Ethernet or other methods.

In an example embodiment, the memory 28 may include one or morenon-transitory memory devices such as, for example, volatile and/ornon-volatile memory that may be either fixed or removable. The memorymay be configured to store information, data, applications, instructionsor the like for enabling the apparatus 20 to carry out various functionsin accordance with example embodiments of the present invention. Forexample, the memory could be configured to buffer input data forprocessing by the processor 24. Additionally or alternatively, thememory could be configured to store instructions for execution by theprocessor. As yet another alternative, the memory may include one of aplurality of databases that may store a variety of files, contents ordata sets. Among the contents of the memory, applications may be storedfor execution by the processor in order to carry out the functionalityassociated with each respective application. In some cases, the memorymay be in communication with the processor via a bus for passinginformation among components of the apparatus.

The processor 24 may be embodied in a number of different ways. Forexample, the processor may be embodied as various processing means suchas one or more of a microprocessor or other processing element, acoprocessor, a controller or various other computing or processingdevices including integrated circuits such as, for example, an ASIC(application specific integrated circuit), an FPGA (field programmablegate array), or the like. In an example embodiment, the processor may beconfigured to execute instructions stored in the memory 28 or otherwiseaccessible to the processor. As such, whether configured by hardware orby a combination of hardware and software, the processor may representan entity (e.g., physically embodied in circuitry—in the form ofprocessing circuitry 22) capable of performing operations according toembodiments of the present invention while configured accordingly. Thus,for example, when the processor is embodied as an ASIC, FPGA or thelike, the processor may be specifically configured hardware forconducting the operations described herein. Alternatively, as anotherexample, when the processor is embodied as an executor of softwareinstructions, the instructions may specifically configure the processorto perform the operations described herein.

In some example embodiments, a burst of a radio frame may be received,such as via the communication interface 26. Upon receipt of the one ormore bursts, the processing circuitry 22, the processor 24 or the like,may be configured to determine an error term for USF symbols in the oneor more bursts, while compensating for the inter symbol interferencecaused by the one or more TSC symbols and/or other symbols in the burst.Using, the location of the TSC symbols and the location of one or moreUSF symbols, the processing circuitry 22, the processor 24, or the like,may determine a weighted error measure for each of the available USFsequences (e.g. there are 8 available USF sequences in EGPRS2). The oneor more weighted error measures for the one or more bursts may beevaluated, such as by the processing circuitry 22, the processor 24 orthe like, for a plurality of available USF sequences or USF symbols. Insome example embodiments, the USF value is determined based on the USFsequence with the lowest weighted error measure.

In some example embodiments, the apparatus, method and computer programproduct may be defined by or otherwise represented as a system model.The system model of some example embodiments, may denote the transmittedsymbols as x=[x₁, . . . , x_(N)]^(T). As such, the received burst attime index n is then given by, for example:

$\begin{matrix}{y_{n} = {{\sum\limits_{i = 0}^{L - 1}{h_{i}x_{n - i}}} + v_{n}}} & (1)\end{matrix}$

where y_(n)=[Y_(n,1), . . . , y_(n,n) _(sps) ]^(T) is the receivedburst, with an example oversampling factor n_(sps). The ith tap in thechannel impulse response with symbol length L is given byh_(i)=[h_(i,1), . . . , h_(i,n) _(sps) ]^(T), and υ_(n) denotes thenoise term at time n. The system model in (1) can be formulated, forexample, as:y=Hx+υ  (2)

where H is the channel matrix of size M×N, while y and υ are vectors ofsize M. Although the system models described with reference to equations(1) and (2) are used to describe some example embodiments, differentvariations or refinements of these models can also be used in otherexample embodiments.

Based on the received burst, N_(u) may define the index in x (e.g.symbol location) where the first USF symbol is present and N_(USF,symb)may represent the number of USF symbols per burst. In some exampleembodiments, the USF symbols may be the symbols x_(USF)=[x_(N) _(u′) ,x_(N) _(u) _(+(N) _(USF,symb) −1)]^(T) where N_(USF,symb)=3 for EGPRS2Aand N_(USF,symb)=4 for EGPRS2B. An index k may be used in some examplesto distinguish between the different bursts in the radio block.

Furthermore, {circumflex over (x)}_(j) ^((k)) is configured to representthe estimated symbols transmitted under the assumption that the jth USFsequence is used. In other words {circumflex over (x)}_(j) ^((k)) couldcontain symbols from the TSC, and/or symbols from the jth of theplurality of the available USF sequences. Alternatively or additionally,different formulations of {circumflex over (x)}_(j) ^((k)) may alsoincorporate the additional data symbols that are located next to or inthe proximity of the USF symbols. As such, {circumflex over (x)}_(j)^((k)) is compared to the received signal and a weighted error measureε_(j) is determined, such as by the processing circuitry 22, theprocessor 24 or the like.

In some example embodiments, the weighted error measure ε_(j) maytypically comprise a combination of squared residual errors for eachburst of the radio frame. As such, given {circumflex over (x)}_(j)^((k)) the weighted error measure ε_(j) arising when using the jth USFsequence (e.g. j denotes that it is the jth admissible USF sequence) maybe calculated as:

$\begin{matrix}{ɛ_{j} = {\sum\limits_{k}{w_{k}{f\left( {y^{(k)},H^{(k)},{\hat{x}}_{j}^{(k)}} \right)}}}} & (3)\end{matrix}$

where w_(k) is a scalar weighting of the kth burst and f(·) is the errorfunction that is configured to calculate, for example, the squaredresidual error with k spanning the bursts that are used in theevaluation of the error measure. Further still, in some examples one ormore bursts may be disregarded if they are heavily corrupted by noise.

In some example embodiments and in an instance in which the noise termis Additive White Gaussian Noise (AWGN), e.g. υ^((k))˜

(0, σ_(k) ²I) where σ_(k) ² denotes the noise variance for the k'thburst and I is the identity matrix, an example error function may berecited as:

$\begin{matrix}\begin{matrix}{{f\left( {y^{(k)},H^{(k)},{\hat{x}}_{j}^{(k)}} \right)} = {\sum\limits_{n = N_{u}}^{N_{u} + N_{1}^{(k)}}{{y_{n}^{(k)} - {\sum\limits_{i = 0}^{L - 1}{h_{i}^{(k)}{\hat{x}}_{j,{n - i}}^{(k)}}}}}^{2}}} \\{= {\sum\limits_{n = N_{u}}^{N_{u} + N_{1}^{(k)}}{e_{j,n}^{(k)}}^{2}}}\end{matrix} & (4)\end{matrix}$

-   -   with the ith tap of the channel impulse response of symbol        length L given by h_(i)=[h_(i,1), . . . , h_(i,n) _(sps) ]^(T).        In equation (4) e_(j,n) ^((k)) represents the residual error        term and N_(u) defines the index in x where the first USF symbol        is present. Alternatively or additionally and in an instance in        which it is determined that the noise is colored, such as by the        processing circuitry 22, the processor 24 or the like, a        prewhitening operation may be applied that is configured to        remove a correlation in the noise. In some example embodiments,        equation (4) may identify symbols to the left of the USF symbols        in a burst, which includes indices n=[N_(u)−L+1, . . . ,        N_(u)−1] in {circumflex over (x)}_(j) ^((k)). As a result, the        ISI from the TSC symbols can be cancelled such as by the        processing circuitry 22, the processor 24 or the like.

In some example embodiments, the positive integer N₁^((k))≦N_(USF,symb)+L−1 specifies the number of symbols used in theerror function in the kth burst. In an instance in which N₁^((k))>N_(USF,symb) is selected, the ISI from data symbols and, in somecases from TSC symbols, will be determined and equation (4) may furtherbe used by the processing circuitry 22, the processor 24 or the like todetermine the error function based on the transmitted symbols positionedadjacent to the USF symbols.

In some example embodiments, the scalar weighting can be set to auniform value implying that each burst is equally weighted.Alternatively or additionally, in an instance in which the noisevariance is determined, such as by the processing circuitry 22, theprocessor 24 or the like, the noise variance may be reflected byw_(k)=1/σ_(k) ². In some example embodiments, other a-priori informationmay also be used by the processing circuitry 22, the processor 24 or thelike when choosing the weighting parameter.

Based on the measurement of the weighted error measure ε_(j), in someexample embodiments, the USF value with the smallest or lowest weightederror measure may be chosen as the detected USF value, for example:

$\begin{matrix}{{{U\; S\; F} = {\arg{\min\limits_{j}ɛ_{j}}}},{j \in \left\{ {1,\ldots\mspace{14mu},N_{{USF},{values}}} \right\}}} & (5)\end{matrix}$

where N_(USF,values) is the number of admissible USF values. For exampleand in some example embodiments the number of admissible USF values inthe GSM communication system may be eight. Alternatively oradditionally, other admissible USF values may be determined in alternatecommunication systems.

In some example embodiments the different weighted error measures ε_(j)for jε{1, . . . , N_(USF,values)} can be compared against each other toensure that the uplink state flag value is reliably detected. In aninstance in which the comparison is made, such as by the processingcircuitry 22, the processor 24 or the like, and the USF value is notreliably detected, then processing circuitry 22, the processor 24 or thelike may be configured to determine the USF value to be invalid. Ininstances in which the USF value is reliably is detected, then the USFvalue may be declared valid. For example, and in some exampleembodiments, the detected USF value can be declared invalid if the ratiobetween the smallest and second smallest weighted error measures doesnot exceed a given threshold.

FIG. 3 a illustrates an example burst structure in DAS-7 to DAS-12.Referring to FIG. 3 a, the vector x_(j) ^((k)) for EGPRS2A consists of:3 tail symbols 32, 58 data symbols 34, 26 TSC symbols 36, 3 USF symbols38, 55 data symbols 40, 3 tail symbols 42 and a guard period 44:

                                                               (6)$x_{j}^{(k)} = {\left\lbrack {{tail}_{1}^{(k)},\ldots\mspace{14mu},{tail}_{3}^{(k)},d_{1}^{(k)},{\ldots\mspace{14mu} d_{58}^{(k)}},t_{1}^{(k)},\ldots\mspace{14mu},t_{26}^{(k)},\underset{\underset{{index}\mspace{14mu} N_{u}}{︸}}{u_{j,1}^{(k)}},u_{j,2}^{(k)},u_{j,3}^{(k)},d_{59}^{(k)},\ldots\mspace{14mu},d_{116}^{(k)},{tail}_{4}^{(k)},\ldots\mspace{14mu},{tail}_{6}^{(k)}} \right\rbrack^{T}.}$where tail_(i) ^((k)) denote the tail symbols, d_(i) ^((k)) the datasymbols, t_(i) ^((k)) the TSC symbols, and u_(j,i) ^((k)) the ith USFsymbol in the jth admissible USF sequence in burst k.

In some example embodiments, the summation of the squared residualerror, ∥e_(j,n) ^((k))∥², may be accomplished over several time indices,i.e. n={N_(u), . . . , N_(u)+N₁ ^((k))}, where N₁ ^((k)) is a positiveinteger N₁ ^((k))≧N_(USF,symb)+L−1, and N_(USF,symb) is the number ofUSF symbols per burst. At the time index n=N_(u), the error may berepresented as:

                                                   (7) $\begin{matrix}{{e_{j,N_{u}}^{(k)}}^{2} = {{{y_{N_{u}}^{(k)} - {\sum\limits_{i = 0}^{L - 1}{h_{i}^{(k)}{\hat{x}}_{j,{N_{u} - i}}^{(k)}}}}}^{2} = {{y_{N_{u}}^{(k)} - \left( {{h_{0}^{(k)}u_{j,1}^{(k)}} + \overset{\overset{{ISI}\mspace{14mu}{part}}{︷}}{\sum\limits_{i = 1}^{L - 1}{h_{i}^{(k)}{\hat{x}}_{j,{N_{u} - i}}^{(k)}}}} \right)}}^{2}}} \\{= {{{y_{N_{u}}^{(k)} - \left( {{h_{0}^{(k)}u_{j,1}^{(k)}} + \underset{\underset{{ISI}\mspace{14mu}{part}}{⎵}}{\left\lbrack {h_{1}^{(k)},\ldots\mspace{14mu},h_{L - 1}^{(k)}} \right\rbrack\begin{bmatrix}t_{26}^{(k)} \\t_{25}^{(k)} \\\vdots \\t_{26 - L + 2}^{(k)}\end{bmatrix}}} \right)}}^{2}.}}\end{matrix}$

In an instance in which n=N_(u) inter symbol interference (e.g. ISIpart) arises from the TSC symbols, t_(q) ₁ ^((k)), where q₁={26−L+2, . .. , 26}, ISI may be cancelled completely when the channel length, L, isshorter than the number of ISI free TSC symbols.

The error contribution may also be determined for time indexn=N_(USF,symb)+L−1

N₂. For EGPRS2A this time index is, N₂=3+(L−1)=L+2, where the error maybe represented as:

                                                   (8) $\begin{matrix}{{e_{j,N_{2}}^{(k)}}^{2} = {{{y_{N_{2}}^{(k)} - {\sum\limits_{i = 0}^{L - 1}{h_{i}^{(k)}{\hat{x}}_{j,{N_{2} - i}}^{(k)}}}}}^{2} = {{y_{N_{2}}^{(k)} - \left( {\overset{\overset{{ISI}\mspace{14mu}{part}}{︷}}{\sum\limits_{i = 0}^{L - 2}{h_{i}^{(k)}{\hat{x}}_{j,{N_{2} - i}}^{(k)}}} + {h_{L - 1}^{(k)}u_{j,3}^{(k)}}} \right)}}^{2}}} \\{= {{y_{N_{2}}^{(k)} - \left( {\underset{\underset{{ISI}\mspace{14mu}{part}}{︸}}{\left\lbrack {h_{0}^{(k)},\ldots\mspace{14mu},h_{L - 2}^{(k)}} \right\rbrack\begin{bmatrix}d_{59 + L - 1}^{(k)} \\\vdots \\d_{61}^{(k)} \\d_{60}^{(k)} \\d_{59}^{(k)}\end{bmatrix}} + {h_{L - 1}^{(k)}u_{j,3}^{(k)}}} \right)}}^{2}}\end{matrix}$

In this example, the ISI is dependent on the second data part in theburst, e.g. the estimated symbols after the USF symbols, d_(q) ₂ ^((k)),where q₂={59, . . . , 58+L}. In this example case, the ISI may becancelled in an instance in which the data symbols next to the USFsymbols have been detected.

In some example embodiments, ISI contribution may depend on the timeindex. For example, an ISI in a first time index may consist both ofknown training sequence symbols, t, and estimated data, d in an instancein which n=N_(u)+N_(USF,symb)

N₃, and the channel length is longer than the number of USF symbols inone burst, i.e. L>N_(USF,symb) (e.g. 3 in EGPRS2A). In such an exampleand assuming that L=5, in that case the error in time index n=N₃ may berepresented as:

$\begin{matrix}\begin{matrix}{{e_{j,N_{3}}^{(k)}}^{2} = {{y_{N_{3}}^{(k)} - {\sum\limits_{i = 0}^{L - 1}{h_{i}^{(k)}{\hat{x}}_{j,{N_{3} - i}}^{(k)}}}}}^{2}} \\{= {{{y_{N_{3}}^{(k)} - \left( {\overset{\overset{{ISI}\mspace{14mu}{part}\mspace{14mu}{from}\mspace{14mu}{data}}{︷}}{h_{0}^{(k)}d_{59}^{(k)}} + {\begin{bmatrix}h_{1}^{(k)} & h_{2}^{(k)} & h_{3}^{(k)}\end{bmatrix}\begin{bmatrix}u_{j,3}^{(k)} \\u_{j,2}^{(k)} \\u_{j,1}^{(k)}\end{bmatrix}} + \overset{\overset{{ISI}\mspace{14mu}{part}\mspace{14mu}{from}\mspace{14mu}{TSC}}{︷}}{h_{4}^{(k)}t_{26}^{(k)}}} \right)}}^{2}.}}\end{matrix} & (9)\end{matrix}$

FIG. 3 b illustrates the burst structure for EGPRS2B in DBS-5 to DBS-12.In EGPRS2B DBS-5 to DBS-12 includes a tail of 4 symbols 50, followed by69 of other user data and/or payload symbols 52, followed by 31 TSCsymbols 54, then 4 USF symbols 56, followed by 65 other user data and/orpayload symbols 58 and then 4 tail symbols 60 before the guard period62.

FIG. 4 illustrate example operations performed by a method, apparatusand computer program product, such as apparatus 20 of FIG. 2 inaccordance with one embodiment of the present invention. It will beunderstood that each block of the flowchart, and combinations of blocksin the flowchart, may be implemented by various means, such as hardware,firmware, processor, circuitry and/or other device associated withexecution of software including one or more computer programinstructions. For example, one or more of the procedures describedherein may be embodied by computer program instructions. In this regard,the computer program instructions which embody the procedures describedherein may be stored by a memory 28 of an apparatus employing anembodiment of the present invention and executed by a processor 24 inthe apparatus. As will be appreciated, any such computer programinstructions may be loaded onto a computer or other programmableapparatus (e.g., hardware) to produce a machine, such that the resultingcomputer or other programmable apparatus provides for implementation ofthe functions specified in the flowchart block(s). These computerprogram instructions may also be stored in a non-transitorycomputer-readable storage memory that may direct a computer or otherprogrammable apparatus to function in a particular manner, such that theinstructions stored in the computer-readable storage memory produce anarticle of manufacture, the execution of which implements the functionspecified in the flowchart block(s). The computer program instructionsmay also be loaded onto a computer or other programmable apparatus tocause a series of operations to be performed on the computer or otherprogrammable apparatus to produce a computer-implemented process suchthat the instructions which execute on the computer or otherprogrammable apparatus provide operations for implementing the functionsspecified in the flowchart block(s). As such, the operations of FIG. 4,when executed, convert a computer or processing circuitry into aparticular machine configured to perform an example embodiment of thepresent invention. Accordingly, the operations of FIG. 4 define analgorithm for configuring a computer or processing circuitry 22, e.g.,processing system, to perform an example embodiment. In some cases, ageneral purpose computer may be provided with an instance of theprocessor which performs the algorithm of FIG. 4 to transform thegeneral purpose computer into a particular machine configured to performan example embodiment.

Accordingly, blocks of the flowchart support combinations of means forperforming the specified functions and combinations of operations forperforming the specified functions. It will also be understood that oneor more blocks of the flowchart, and combinations of blocks in theflowchart, can be implemented by special purpose hardware-based computersystems which perform the specified functions, or combinations ofspecial purpose hardware and computer instructions.

In some embodiments, certain ones of the operations herein may bemodified or further amplified as described below. Moreover, in someembodiments additional optional operations may also be included. Itshould be appreciated that each of the modifications, optional additionsor amplifications below may be included with the operations hereineither alone or in combination with any others among the featuresdescribed herein.

As is shown with respect to operation 72, the apparatus 20 embodied, forexample by a communications device 10, may include means, such as theprocessing circuitry 22, the processor 24, the communication interface26 or the like, for receiving one or more bursts, the one or more burstscomprising a radio block. As is shown with respect to operation 74, theapparatus 20 embodied, for example by a communications device 10, mayinclude means, such as the processing circuitry 22, the processor 24, orthe like, for determining a location of one or more uplink state flagsymbols in the burst transmission.

As is shown with respect to operation 76, the apparatus 20 embodied, forexample by a communications device 10, may include means, such as theprocessing circuitry 22, the processor 24, or the like, for determiningone or more residual error terms by jointly detecting and decoding inone or more bursts of a radio block, wherein the one or more residualerror terms are determined over a plurality of uplink state flag symbolsin the one or more bursts that correspond to a plurality of availableuplink state flag sequences. In some examples, the apparatus 20embodied, for example by a communications device 10, may further includemeans, such as the processing circuitry 22, the processor 24, or thelike, for determining inter symbol interference based on at least one ofa plurality of training sequence code symbols or one or more datasymbols in the one or more bursts of the radio block. In some exampleembodiments, the one or more residual error terms are determined bycompensating for the inter symbol interference of the training sequencecode symbols or the one or more data symbols. The one or more datasymbols may comprise the estimated bits or symbols other than thosesymbols that represent the uplink state flag sequence.

As is shown with respect to operation 78, the apparatus 20 embodied, forexample by a communications device 10, may include means, such as theprocessing circuitry 22, the processor 24, or the like, for determininga weighted error measure for each of the plurality of available uplinkstate flag sequences based on the one or more residual error terms. Asis shown with respect to operation 80, the apparatus 20 embodied, forexample by a communications device 10, may include means, such as theprocessing circuitry 22, the processor 24, or the like, for determiningan uplink state flag value based on the plurality of weighted errormeasures.

As is shown with respect to operation 82, the apparatus 20 embodied, forexample by a communications device 10, may include means, such as theprocessing circuitry 22, the processor 24, or the like, for determiningthat the uplink state flag value is reliably detected. As is shown withrespect to operation 84, the apparatus 20 embodied, for example by acommunications device 10, may include means, such as the processingcircuitry 22, the processor 24, the communication interface 26 or thelike, for causing a transmission of data.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Moreover, although the foregoing descriptions and the associateddrawings describe example embodiments in the context of certain examplecombinations of elements and/or functions, it should be appreciated thatdifferent combinations of elements and/or functions may be provided byalternative embodiments without departing from the scope of the appendedclaims. In this regard, for example, different combinations of elementsand/or functions than those explicitly described above are alsocontemplated as may be set forth in some of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

That which is claimed is:
 1. A method comprising: identifying, withcircuitry, a plurality of uplink state flag symbols in one or morebursts of a radio block, the plurality of uplink state flag symbolscorresponding to a plurality of available uplink state flag sequences;determining, with the circuitry, one or more residual error terms byjointly detecting and decoding the one or more bursts, the one or moreresidual error terms being determined over the plurality of uplink stateflag symbols; determining, with the circuitry, a weighted error measurefor each of the plurality of available uplink state flag sequences basedon the one or more residual error terms; and determining, with thecircuitry, an uplink state flag value based on the plurality of weightederror measures.
 2. A method according to claim 1, further comprising:determining inter symbol interference based on at least one of aplurality of training sequence code symbols or one or more data symbolsin the one or more bursts of the radio block.
 3. A method according toclaim 2, wherein the one or more residual error terms are determined bycompensating for the inter symbol interference of the training sequencecode symbols or the one or more data symbols.
 4. A method according toclaim 2, wherein the inter symbol interference determined from at leastthe training sequence code and/or the one or more data symbols isconfigured to be cancelled based on the determined one or more residualerror terms.
 5. A method according to claim 3, wherein the one or moredata symbols comprise estimated bits or symbols other than those datasymbols that represent the uplink state flag sequence.
 6. A methodaccording to claim 1, further comprising: selecting the uplink stateflag sequence based on a smallest weighted error measure associated withthe plurality of available uplink state flag sequences.
 7. A methodaccording to claim 6, further comprising: determining that the selecteduplink state flag sequence matches an allocated uplink state flagsequence; and causing a transmission of data.
 8. A method according toclaim 1, further comprising: determining that the uplink state flagvalue is reliably detected.
 9. An apparatus comprising: circuitryconfigured to identify a plurality of uplink state flag symbols in oneor more bursts of a radio block, the plurality of uplink state flagsymbols corresponding to a plurality of available uplink state flagsequences; determine one or more residual error terms by jointlydetecting and decoding the one or more bursts, the one or more residualerror terms being determined over the plurality of uplink state flagsymbols; determine a weighted error measure for each of the plurality ofavailable uplink state flag sequences based on the one or more residualerror terms; and determine an uplink state flag value based on theplurality of weighted error measures.
 10. An apparatus according toclaim 9, wherein the processing system is arranged to cause theapparatus to: determine inter symbol interference based on at least oneof a plurality of training sequence code symbols or one or more datasymbols in the one or more bursts of the radio block.
 11. An apparatusaccording to claim 10, wherein the one or more residual error terms aredetermined by compensating for the inter symbol interference of thetraining sequence code symbols or the one or more data symbols.
 12. Anapparatus according to claim 10, wherein the inter symbol interferencefrom at least the training sequence code and/or the one or more datasymbols is configured to be cancelled based on the determined one ormore residual error terms.
 13. An apparatus according to claim 11,wherein the one or more data symbols comprise estimated bits or symbolsother than those data symbols that represent the uplink state flagsequence.
 14. An apparatus according to claim 9, wherein the processingsystem is arranged to cause the apparatus to: select the uplink stateflag sequence based on a smallest weighted error measure associated withthe plurality of available uplink state flag sequences.
 15. An apparatusaccording to claim 14, wherein the processing system is arranged tocause the apparatus to: determine that the selected uplink state flagsequence matches an allocated uplink state flag sequence; and cause atransmission of data.
 16. An apparatus according to claim 9, wherein theprocessing system is arranged to cause the apparatus to: determine thatthe uplink state flag value is reliably detected.
 17. An apparatusaccording to claim 9, wherein the apparatus comprises at least one of auser equipment or a communications device.
 18. An apparatus according toclaim 9, wherein the apparatus is configured for use in at least one ofglobal system for mobile communications, wideband code division multipleaccess, time division synchronous code division multiple access, a longterm evolution or long term evolution advanced system.
 19. Anon-transitory computer-readable medium encoded with computer-readableinstructions that when executed by a processor, cause the processor toperform a method comprising: identifying a plurality of uplink stateflag symbols in one or more bursts of a radio block, the plurality ofuplink state flag symbols corresponding to a plurality of availableuplink state flag sequences; determining one or more residual errorterms by jointly detecting and decoding the one or more bursts, the oneor more residual error terms being determined over the plurality ofuplink state flag symbols; determine a weighted error measure for eachof the plurality of available uplink state flag sequences based on theone or more residual error terms; and determine an uplink state flagvalue based on the plurality of weighted error measures.
 20. Thenon-transitory computer-readable medium according to claim 19, furthercomprising: determining inter symbol interference based on at least oneof a plurality of training sequence code symbols or one or more datasymbols in the one or more bursts of the radio block.